Zoom lens system

ABSTRACT

The zoom lens system of this invention is capable of extreme close-up photography, and consists mainly of a focusing lens group having positive refractive power and a negative refractive power variator. The variator is divided into a positive refractive power lens group and a negative refractive power lens group. In phototaking from the infinity to a normal distance, said focusing lens group is shifted for focusing and for focusing a subject located closer than said normal distance, the variator is held in telephoto position and then the positive refractive power lens group of the variator is shifted forward for focusing.

United 51 Someya [54] ZOOM LENS SYSTEM [72] Inventor: Atsushi Somcya,Tokyo. Japan [73] Assignee: Canon Kabushlkl Kalsha, Tokyo, Japan [22]Filed: June 29, 1970 [Zl] Appl. No: 50,675

W [451 May 9, 1972 3.348.899 l0/l967 Price ..350/l84 3,030,863 4/l962Schwartz et a] ..350/l84 Primary Examiner-David Schonberg AssistantExaminer-Paul A. Sacher Allorney-Joseph M. Fitzpatrick [57] ABSTRACT Thezoom lens system of this invention is capable of extreme close-upphotography, and consists mainly of a focusing lens group havingpositive refractive power and a negative refractive power variator. Thevariator is divided into a positive refractive power lens group and anegative refractive power lens group. In phototaking from the infinityto a normal distance, said focusing lens group is shifted for focusingand for focusing a subject located closer than said normal distance, thevariator is held in telephoto position and then the positive refractivepower lens group of the va; iator is shifted forward for focusing.

2 Clalns, 7 Drawing F lgurr PATENTEDMAY 9:912

SHEEI 2 BF 3 FIG. 5

PATENTEBMAY 9 I972 3,661,445

Si-LFJEI 3 OF 3 FIG. 6

ZOOM LENS SYSTEM This invention relates to a zoom lens system which iscapable of extreme close-up photography.

In the conventional zoom lens system, the whole or a part of the frontlens group is moved for close-up photography.

However, for extreme-close-up photography, the aperture or diameter ofthe focusing lens group must be remarkably increased so that thecorrection of optical aberrations becomes extremely difficult. In theconventional zoom lens system, the closest focus is generally of theorder of 1,000 mm and a closeup lens or the like must be attached forphotography of a subject closer than this distance.

The present invention is therefore concerned to a zoom lens system whichcan eliminate the defects as described above and can make anextreme-close-up photography without using any close-up lens attachment.

The present invention provides a zoom lens system comprising a positiverefractive power lens group and a negative refractive power variatorlens group arranged in this order, in which said negative variator lensgroup comprises a positive and negative refractive power lens groupsarranged in this order so that in zooming, both of said positive andnegative lens groups are shifted while the distance therebetween remainsunchanged, thereby varying a focal length; in photography from theinfinity to a normal distance, said focusing lens group is shifted forfocusing; and for focusing a subject located closer than said normaldistance, said variator lens group is once held in telephoto positionand then said positive lens group of said variator lens group is shiftedforward for focusmg.

FIG. 1 is a diagrammatic view illustrating the principle of the zoomlens system in accordance with the present invention;

FIG. 2 is a view similar to FIG. 1 illustrating that of conventionalzoom lens system;

FIG. 3 is for explanation of image focusing in the zoom lens systemdepicted in FIG. 1;

FIG. 4 is a graph illustrating the relationship between a distancebetween the principal points of the front and back lens groups of thevariator lens groups of the zoom lens system in accordance with thepresent invention and a final image point;

FIG. 5 is a graph illustrating the relationship between the distance ofsaid principal points and a magnification;

FIG. 6 is a graph illustrating the relationship between a final pointand a shift of the variator lens group of the conventional zoom lenssystem from the end of telephoto position; and

FIG. 7 is a graph illustrating the relationship between a magnificationand said shift.

Referring now to FIG. 1, L is a focusing lens having positive refractivepower; L is a lens having positive refractive power and L, is a lenshaving negative refractive power and the lenses L, and L comprising as awhole a variator lens group having negative refractive power; L is acompensator lens for compensating the position of the focal point; andL, and L, form a relay lens group. In a zooming operation, the variatorlens group L,, L is moved in the direction indicated by the broken arrowwhile the relative distance between the lenses L, and L remainsunchanged, thereby varying the focal length of the whole zooming lenssystem. In focusing from infinity to a normal phototaking distance, thefocusing lens L, is shifted in the direction indicated by the arrow.

On the other hand, in case of more close-up photography in accordancewith the present invention, the variator lens group is once held intelephoto position and then only the positive refractive power lens L,is shifted forward as shown by the solid arrow for focusing.

In case of the zoom lens system in which the positive refractive powerfocusing lens and the negative refractive power variator lens group arearranged in this order, the photo-taking magnification is increased whenthe negative refractive power variator lens group is shifted backward.It is therefore most advantageous for extreme-close-up photography tomove the variator lens group to its backmost position in order to obtainthe largest magnification. The present invention not only utilizes thisprinciple but also is based upon the efiective constitution that thenegative refractive power variator lens group is made of the positiveand negative lenses as discussed hereinabove, so that after the negativevariator lens group L,, L, as a whole is shifted to the backmostposition, the positive front lens is shifted forward forextreme-close-up focusing.

The reason why such extreme-close-up photography with largemagnification is possible in accordance with the present invention willbe described in more detail hereinafter with reference to FIG. 3.

In FIG. 3, 5,, S, and S, and S S, and S, designate the distances betweenthe objects and images formed by the lenses L,, L, and L respectively;e, the distance between the principal points of the lenses L, and L 1,the distance between the principal points of the lenses L and L and f f,and f,, the focal lengths of the lenses L, L, and L, respectively.

Assuming that the magnification obtained by the lenses L,, L, and L, beM, the following relations may be held:

The above equations are plotted as shown in FIGS. 4 and 5. To simplifythe discussion, we assume that e 0 when the lenses L, and L, are movedtoward each other most closely. From FIG. 4, it will be seen that S, isincreased as e is increased from 0 to a positive value, and S becomesfinally infinity. In this case, S l f,. When e is further increased, thevalue of S becomes negative and within the focal length L. Until e 2f,8,, it is possible to decrease the value of [S,| In this case, when thefocal length L, is so determined as to satisfy the relation f: 3).focusing becomes possible until S 0.

The quadratic equation (2) may be rewritten as below:

M A e Be c} Hence,

dMlde=A (2+B) 4 Since A 0 and the value of e which gives the minimumvalue c (8/2) 0 and therefore, dM/de 0 for all of the values of e 0.That is, the magnification value M is increased as e is increased. Thediscriminant of Eq. (3)

D B 4C 0 so that M is positive or negative. However, in the presentinvention, M must be positive. Therefore, in order to effectivelyincrease M within the range of e 0, the value of C must be selected asto satisfy C E 0. As shown in FIG. 5, M is always positive for e 0 andincreases in a very effective manner.

PRIOR ART The conventional zoom lens in illustrated in FIG. 2, in whichthe positive refractive power focusing lens L,, the negative refractivepower variator lens group L the compensator lens L and the relay lensgroup L, and I. are arranged in this order. For focusing at a relativelyshort distance, only the where 5 distance between the object and thelens group L 51., distance between the image and this lens group; and

f focal length of this lens group.

Equations (5) and (6) are plotted as shown in FIGS. 6 and 7. It is seenthat both of S, and M increase linearly as l increases.

Therefore. the conventional zoom lens system is remarkably inferior tothe system of the present invention in which S, and M varyquadratically.

The data of one example of the zoom lens system in accordance with thepresent invention is shown in Table 1. The zoom lens is for Cine cameraswith a zoom ratio of 8:1 and a compound focal length of 58 mm. In thetable e denotes the distance between the principal points of theadjacent lens groups at its telephotoposition having the focal lengthsf.

Compound focal length 58 The lenses L, and L are shifted by 5.0 and 35.0mm respectively, and then Magnification through lenses L, through L 1.61Magnification through lenses L, through L, 0.47 Distance between thesubject and the first lens groups S, 1 37.5

S, (ed-49.152) 10,000/8-83221) The example of the conventional zoom lensillustrated in FIG. 2 is shown in Table 11.

TABLE 11 Compound focal length 58 mm When the first lens L, is shiftedby 5.0 mm, then magnification magnification through L, L, m 0.061

distance between the subject and the first lens 5, =1,0l2.4 M=0.0427(l-46.963)

From the above comparison the extreme-close-up photography hithertounobtainable by the conventional zoom lens system is now possible by thezoom lens of the present invention with a greater magnification.Furthermore, the zoom lens of the present invention is similar in sizeto the conventional zoom lens system.

What is claimed is:

1. In a zoom lens system, a focusing lens component having a positiverefractive power, a variator lens component having a negative refractivepower, a compensator lens component for compensating focal pointposition, and a relay lens com ponent, said variator lens componentcomprising a positive refractive power lens and a negative refractivepower lens, the focusing lens component being shiftable toward an objectto be photographed and the positive refractive power lens and thenegative refractive power lens of the variator lens component beingshiftable as a unit toward the object, while the distance between thepositive and the negative lenses remains unchanged to provide focusingfrom infinity to a normal phototaking distance and said positive lens ofthe variator lens component being shiftable by itself further toward theobject for focusing from said normal phototaking distance to an extremeclose-up distance.

2. A zoom lens system according to claim 1, wherein there is maintainedthe following relationships:

and

5,, S, and S; and 5,, S, and S being the distances between the objectsand images formed by the focusing lens (L,), the positive refractivepower lens (L and the negative refractive power lens (L respectively. ebeing the distance between the principal points of the lens groups 1.and L 1 being the distance between the principal points of the lensgroups L, and L;,,f,,f, andf being the focal lengths of the lenses L, L,and L respectively, and M being the magnification obtained by the lensesL,, L, and L t i i

1. In a zoom lens system, a focusing lens component having a positiverefractive power, a variator lens component having a negative refractivepower, a compensator lens component for compensating focal pointposition, and a relay lens component, said variator lens componentcomprising a positive refractive power lens and a negative refractivepower lens, the focusing lens component being shiftable toward an objectto be photographed and the positive refractive power lens and thenegative refractive power lens of the variator lens component beingshiftable as a unit toward the object, while the distance between thepositive and the negative lenses remains unchanged to provide focusingfrom infinity to a normal phototaking distance and said positive lens ofthe variator lens component being shiftable by itself further toward theobject for focusing from said normal phototaking distance to an extremeclose-up distance.
 2. A zoom lens system according to claim 1, whereinthere is maintained the following relationships: S1, S2 and S3 and S1'',S2'' and S3'' being the distances between the objects and images formedby the focusing lens (L1), the positive refractive power lens (L2) andthe negative refractive power lens (L3), respectively, e being thedistance between the principal points of the lens groups L2 and L3, lbeing the distance between the principal points of the lens groups L1and L3, f1, f2 and f3 being the focal lengths of the lenses L1 L2 andL3, respectively, and M being the magnification obtained by the lensesL1, L2 and L3.